fix schema rule (#1059)

docs-2.0/3.ngql-guide/10.tag-statements/1.create-tag.md

@@ -31,7 +31,7 @@ CREATE TAG [IF NOT EXISTS] <tag_name>
 |Parameter|Description|
 |:---|:---|
 |`IF NOT EXISTS`|Detects if the tag that you want to create exists. If it does not exist, a new one will be created. The tag existence detection here only compares the tag names (excluding properties).|
-|`<tag_name>`|The tag name must be **unique** in a graph space. Once the tag name is set, it can not be altered. The name of the tag supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
+|`<tag_name>`|The tag name must be **unique** in a graph space. Once the tag name is set, it can not be altered. The name of the tag starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`<prop_name>`|The name of the property. It must be unique for each tag. The rules for permitted property names are the same as those for tag names.|
 |`<data_type>`|Shows the data type of each property. For a full description of the property data types, see [Data types](../3.data-types/1.numeric.md) and [Boolean](../3.data-types/2.boolean.md).|
 |`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`.|

docs-2.0/3.ngql-guide/11.edge-type-statements/1.create-edge.md

@@ -31,7 +31,7 @@ CREATE EDGE [IF NOT EXISTS] <edge_type_name>
 |Parameter|Description|
 |:---|:---|
 |`IF NOT EXISTS`|Detects if the edge type that you want to create exists. If it does not exist, a new one will be created. The edge type existence detection here only compares the edge type names (excluding properties).|
-|`<edge_type_name>`|The edge type name must be **unique** in a graph space. Once the edge type name is set, it can not be altered. The name of the edge type supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
+|`<edge_type_name>`|The edge type name must be **unique** in a graph space. Once the edge type name is set, it can not be altered. The name of the edge type starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`<prop_name>`|The name of the property. It must be unique for each edge type. The rules for permitted property names are the same as those for edge type names.|
 |`<data_type>`|Shows the data type of each property. For a full description of the property data types, see [Data types](../3.data-types/1.numeric.md) and [Boolean](../3.data-types/2.boolean.md).|
 |`NULL \| NOT NULL`|Specifies if the property supports `NULL | NOT NULL`. The default value is `NULL`.|

docs-2.0/3.ngql-guide/14.native-index-statements/1.create-native-index.md

@@ -70,7 +70,7 @@ CREATE {TAG | EDGE} INDEX [IF NOT EXISTS] <index_name> ON {<tag_name> | <edge_na
 |:---|:---|
 |`TAG \| EDGE`|Specifies the index type that you want to create.|
 |`IF NOT EXISTS`|Detects if the index that you want to create exists. If it does not exist, a new one will be created.|
-|`<index_name>`|The name of the index. It must be unique in a graph space. A recommended way of naming is `i_tagName_propName`. The name of the index supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
+|`<index_name>`|The name of the index. It must be unique in a graph space. A recommended way of naming is `i_tagName_propName`. The name of the index starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`<tag_name> \| <edge_name>`|Specifies the name of the tag or edge associated with the index.|
 |`<prop_name_list>`|To index a **variable-length** string property, you must use `prop_name(length)` to specify the index length. To index a tag or an edge type, ignore the `prop_name_list`.|
 |`COMMENT`|The remarks of the index. The maximum length is 256 bytes. By default, there will be no comments on an index.|

docs-2.0/3.ngql-guide/9.space-statements/1.create-space.md

@@ -26,7 +26,7 @@ zone_list:
 |Parameter|Description|
 |:---|:---|
 |`IF NOT EXISTS`|Detects if the related graph space exists. If it does not exist, a new one will be created. The graph space existence detection here only compares the graph space name (excluding properties).|
-|`<graph_space_name>`|Uniquely identifies a graph space in a Nebula Graph instance. The name of the graph space supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
+|`<graph_space_name>`|Uniquely identifies a graph space in a Nebula Graph instance. The name of the graph space starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. To use special characters or reserved keywords as identifiers, quote them with backticks. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).|
 |`partition_num`|Specifies the number of partitions in each replica. The suggested number is five times the number of the hard disks in the cluster. For example, if you have 3 hard disks in the cluster, we recommend that you set 15 partitions. The default value is 100.|
 |`replica_factor`|Specifies the number of replicas in the cluster. The suggested number is 3 in a production environment and 1 in a test environment. The replica number must be an **odd number** for the need of quorum-based voting. The default value is 1.|
 |`vid_type`|A required parameter. Specifies the VID type in a graph space. Available values are `FIXED_STRING(N)` and `INT64`. `INT` equals to `INT64`. `FIXED_STRING(<N>)` specifies the VID as a string, while `INT64` specifies it as an integer. `N` represents the maximum length of the VIDs. If you set a VID that is longer than `N` characters, Nebula Graph throws an error.|
@@ -61,7 +61,7 @@ CREATE SPACE <new_graph_space_name> AS <old_graph_space_name>;
 
 | Parameter | Description |
 | :--- | :--- |
-| `<new_graph_space_name>` | The name of the graph space that is newly created. The name of the graph space supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md). When a new graph space is created, the schema of the old graph space `<old_graph_space_name>` will be cloned, including its parameters (the number of partitions and replicas, etc.), Tag, Edge type, native indexes, and zone. |
+| `<new_graph_space_name>` | The name of the graph space that is newly created. The name of the graph space starts with a letter, supports 1 to 4 bytes UTF-8 encoded characters, such as English letters (case-sensitive), digits, and Chinese characters, but does not support special characters except underscores. For more information, see [Keywords and reserved words](../../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md). When a new graph space is created, the schema of the old graph space `<old_graph_space_name>` will be cloned, including its parameters (the number of partitions and replicas, etc.), Tag, Edge type, native indexes, and zone. |
 | `<old_graph_space_name>` | The name of the graph space that already exists. |
 
 ## Examples